A Russian border guard ship has rammed a Ukrainian vessel as a dramatic chase unfolded in the Black Sea. Three Ukrainian ships were seized after they entered Russia’s territorial waters without proper notification.

The video taken from one of the Russian ships shows the moment two Ukraine’s artillery boats and a tugboat were maneuvering dangerously close to Russia’s vessels.

The incident came as the Ukrainian Navy ships crossed into the Russian territorial waters without authorization, seeking to pass through the Kerch Strait that separates Crimea from the Russian mainland. The actions of the Ukrainian vessels prompted the Russian border guards to intervene.

More detailed footage later circulated online, giving a glimpse on the situation from the sailors’ perspective. The crew of the Russian ship saw their vessel move dangerously close to a smaller Ukrainian one, its bow turning directly towards the Ukrainian vessel. It became clear that the collision was imminent, despite Russian sailors trying hard to prevent it. In seconds the Russian ship rammed into the Ukrainian vessel, but luckily, it somehow remained afloat.

The Ukranian ships were sailing between two Ukrainian ports: from Odessa in the Black Sea to Mariupol in the Azov Sea. The only waterway that connects these is the Kerch Strait. Kiev says it notified Moscow in advance that its navy ships would be sailing through the area.

Moscow denies that it was given any warning, forcing the Russian military to use weapons to stop the vessels. The three Ukrainian ships were then seized and towed to the Kerch port, according to the Russian Security Service (FSB).

While both Russia and Ukraine have freedom of navigation in the Kerch Strait under a 2003 treaty, there are detailed technical rules on how vessels should pass through the narrow, complex waterway. All traffic in the area is controlled by the Crimean sea port of Kerch, and every ship should contact the facility, report her route and destination, and receive permission to sail through the Strait.

As tensions escalated around the situation in the Kerch Strait, Russia called an emergency UN Security Council meeting, while Ukrainian President wants to declare martial law, pending approval by the national parliament.